These three variables have such importance when we prepare to exercise. Lighting refers to appropriate illumination of the area where you are gonna exercise, which is mandatory, that way you will avoid possible injuries that can happen if you don't see well. In addition, pollution is important to consider because refers to the contamination in the training zone, if the air, soil or water is too contaminated to polluted, then you must not train, because your health can get worse.
At last, traffic is important, especially when you are gonna do running trainings, because traffic can cause you injuries or cardiorespiratory problems due to the dioxide carbon that cars, buses, trucks emit.
A carrier could be a person that is infected with a disease and agent but doesn't show any symptoms of it. there is a genetic carrier which is a person or an organism that inherited a trait or mutation through genetics but doesn't show any symptoms
